This keeps happening, on both rims: the tube develops bulges on either side of the stem along the seam where the reenforcing rubber mets the regular tube body. One of these bulges then tears.
This has been plaguing me for a while. I've installed new rim tape, given up on using valve nuts, searched the rims for burrs, verified the rim is drilled for presta, and moved a size up in tubes (tyres are 28mm, switched from 23-28mm tubes to 28-32mm tubes).
As none of that has worked, I've settled on blaming my floor pump. It is older, and it is rather difficult to install and remove it from the stem. At least, I *think* it is difficult to remove. This is my first foray with presta stems, and I'm not quite sure what the norm is.
Does this look like something a crufty, hard and/or tight fitting floor pump could cause? Money is a bit tight, and I'd rather not replace it if it is only an inconvenience for me and not the culprit.